After getting to the Checkpoint just after the first Football Cannon, you'll eventually come across a Stamper. Just behind him on the wall is a portion of the wall you can Punch down. This reveals and alcove with a Bot inside of it.

Checkpoint 4 is just after the previously-mentioned Bot. Here, cross the collapsing bridge and then look right to see a side-path with sinking islands and fire vents. Get to the end of this path for Bot #4.

Checkpoint 5 is followed by a platforming section where you have to jump over cannonballs. Jump onto the cannon at the end of this section and punch down the metal walls of the tower to reveal this Bot.

Shortly after Bot #7 is the last one of the level. Defeat the Spiky near the Star Coin, then headbutt the metal beam with the Impact Plate on it. Run up the beam to the top of the structure it fell onto to rescue Bot #8!